The Impact of Drainage Infrastructure on the Natural Hydrologic Processes of Coastal Tidal Watersheds
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Brown, Christopher
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Abstract
This study analyzed the impact of drainage infrastructure on the natural stormwater patterns and hydrology within an altered first-order tidal creek-ditch system in Hollywood, SC. The objectives were to: 1) quantify changes in flow routing and stormwater volumes due to infrastructure; 2) model tidal influence within the ditch; 3) characterize the differences in hydraulic geometry between natural and altered tidal systems; and 4) analyze the impact of multiple inputs in terms of creek response expressed as excess stage. GIS analysis showed that basin size was changed in 49/53 sub-watersheds due to infrastructure, with 16 of them experiencing >20% change in their natural runoff volumes for a 2-yr, 24-hr storm event (106 mm). Models predicting tidal influence within the partially tidal ditch system indicate that tidal influence has increased since 1993 and will move towards a tidally dominant system by 2050. The unnatural morphology and restrictions along the system have altered expected flow rates, as observations don’t fit previous models created for natural tidal systems. Storm hydrographs and the observed excess stage displayed complex relationships between system response and storm characteristics, with storm size, prior rainfall totals, peak rainfall intensity, and when that intensity occurs within the tidal cycle being significant factors. Precipitation events as low as 7.6 mm resulted in an observable excess stage in the system.